1. Technical Field
The present invention relates to a driving circuit, a driving method, a solid-state imaging device, and an electronic apparatus.
2. Related Art
In a driving circuit such as an output buffer circuit formed of CMOS, when a voltage amplitude greater than a withstanding voltage ΔVlim of a transistor is necessary, a voltage greater than the withstanding voltage is applied to a gate oxide film of the transistor and thus the gate oxide film is broken down, thereby reducing the reliability.
For example, as shown in FIG. 18, in an output buffer circuit having a PMOS transistor Mp101 and an NMOS transistor Mn101 connected in series between a node of a low voltage (such as a ground voltage) VL and a node of a high voltage VH, it is considered that a drive for output is made with a voltage amplitude VL→VH (VH−VL>ΔVlim) greater than the withstanding voltage ΔVlim. For the purpose of simplicity, inversion logics are used in the output buffer circuit according to Related Example 1 shown in FIG. 18. Input and output waveforms are shown in FIG. 19 and device sections at IN=VH and IN=VL are shown in FIGS. 20A and 20B, respectively.
When a drive for an output OUT is made with the low voltage VL, the high voltage VH is applied to the gate electrode of the NMOS transistor Mn101 and the low voltage VL is applied to the drain, the source, and the channel of the transistor Mn101. Accordingly, a voltage VH−VL greater than the withstanding voltage ΔVlim is applied to the gate oxide film, thereby causing a breakdown of the gate oxide film. Since a voltage greater than the withstanding voltage ΔVlim is applied across the gate and drain electrodes of the PMOS transistor Mp101, the breakdown of the gate oxide film thereof is caused.
Similarly, when a drive for the output OUT is made with the high voltage VH, a voltage greater than the withstanding voltage is applied to the gate oxide film of the PMOS transistor Mp101 or across the gate and drain electrodes of the NMOS transistor Mn101, thereby causing the breakdown of the gate oxide film.
In the circuit configuration of the output buffer circuit according to Related Example 1, a high-voltage process such as a MOS device having a thick gate oxide film need be applied to at least the transistors Mp101 and Mn101 of the output terminal. However, the high-voltage process generally causes a problem with an increase in manufacturing cost or an increase in mounting area.
On the other hand, as shown in FIG. 21, an output buffer circuit is known which can make a drive with a voltage amplitude VL→VH greater than the withstanding voltage without using the high-voltage process by connecting a PMOS transistor Mp102 and an NMOS transistor Mn102 having bias voltages VS and VD applied to the gate electrodes thereof in series between the driving transistors Mp101 and Mn101 on the output terminal side of the output buffer circuit (for example, see JP-A-H10-294662). The input and output waveforms of the output buffer circuit according to Related Example 2 are shown in FIG. 22 and device sections at IN=VH and IN=VL are shown in FIGS. 23A and 23B, respectively.
Here, the bias voltage VD is a voltage within the withstanding voltage from the low voltage VL and the bias voltage VS is a voltage within the withstanding voltage from the high voltage VH. In addition, regarding the amplitude of the gate input of the driving transistors Mp101 and Mn101, a drive with VL→VD is made in the NMOS transistor Mn101 and a drive with VS→VH is made in the PMOS transistor Mp101, via the level shifters 101 and 102, respectively. Here, the bias transistors Mp102 and Mn102 to which the bias voltages VS and VD are applied have a function of preventing an output voltage from being directly applied to the drain electrodes of the driving transistors Mp101 and Mn101 at the time of turning off the driving transistors to allow the gate-drain voltage to be greater than the withstanding voltage.
When the input IN is at a high potential, the bias voltage VS is applied to the gate electrode of the PMOS driving transistor Mp101. Accordingly, the high voltage VH is output as the output voltage OUT. At this time, the potential of the drain electrode of the NMOS driving transistor Mn101 is VD−Vthn which is smaller by a voltage of about a threshold value Vthn than the bias voltage VD. Accordingly, VH−VD (≦ΔVlim) is applied to the gate oxide film of the bias transistor Mn102 in maximum and (VD−Vthn)−VL (≦ΔVlim) is applied to the gate oxide film of the PMOS driving transistor Mn101 in maximum, which are smaller than the withstanding voltage.
The same is true when the input IN is at the low potential. That is, since the bias voltage VD is applied to the gate electrode of the NMOS driving transistor Mn101, the low voltage VL is output as the output voltage OUT. At this time, the drain potential of the PMOS driving transistor Mp101 is VS−Vthp which is greater by a voltage of about the threshold voltage Vthp than the bias voltage VS. Accordingly, VS−VL (≦ΔVlim) is applied to the gate oxide film of the bias transistor Mp102 in maximum and VH−(VS−Vthp) (≦ΔVlim) is applied to the gate oxide film of the NMOS driving transistor Mn101 in maximum, which are smaller than the withstanding voltage.